The present invention differs from the refrigerator disclosed in the above mentioned application in a number of respects. The refrigerator of the present invention is a hybrid in that the slide connected to the displacer is always subjected at one end to a pressure intermediate the high and low pressures to which the displacer is subjected. There is no axial central passage in the slide connected to the displacer of the present invention. The present invention provides for a displacer having minimal eccentric forces applied thereto when in the hybrid mode and no eccentric forces when in the fluidic mode whereby it may be of a larger diameter with only one bearing.
There is a need for a cryogenic refrigerator which can operate in magnetic fields which are of a magnitude whereby the field would interfere with proper operation of an electrical synchronous motor. An example of a device having such a field is a nuclear magnetic resonance body scanner. In such a device, the refrigerator cools the shields around a super conducting magnet. The refrigerator in said pending application cannot operate in such a field. The present invention may operate in such a field.